Various technologies have recently been developed as potential successors to the cathode ray tube (CRT). These technologies for the most part are flat panels comprising a large matrix of individually activated pixels which are used to form an image. In general these pixels are arranged into basic units which are repeated throughout the display surface known as the pixel pattern. Full color images are possible using these displays when the pixel pattern consists of at least one red, one green and one blue subpixel.
A matrix display, in its simplest form, comprises square subpixels arranged in a grid to permit addressing select lines to run in straight lines between the subpixels. This arrangement suffers in visual performance, however, because it injects aspects of the grid as pattern noise (tessellations) into the rendered image. This noise is particularly troublesome because the human visual system is acutely sensitive to periodic spatial frequency on the cardinal axes (vertical and horizontal).
One method of eliminating the appearance of tessellations produced by the grid is to increase the resolution of the display to the point at which the noise is beyond the threshold of detection. However, this solution requires increased complexity and associated costs and has practical physical limits. The delta arrangement is an alternative solution for increasing the apparent image quality without increasing the resolution.
In its simplest form, the delta arrangement consists of a modified grid in which every other row is shifted one-half element. While this simple shifted row delta pattern is an improvement over the grid arrangement, it still retains some of the deficiencies of the original grid pattern. One of these deficiencies is the pattern noise created by the square elements themselves. This noise patterning can be detected, for example, on image boundaries that are aligned with a row of the delta pattern display.
Another limitation of the shifted row delta configuration relates to the equal size of the subpixel color elements. Since the human visual system's spatial acuity is not constant with wavelength, certain color display subpixels contribute more to spatial image quality while other color subpixel elements contribute more directly to chromatic image quality. It would, therefore, be an advantage to be able to optimize spatial image quality by allocating a larger spatial area to the subpixel which contributes most to spatial image quality.
When red, green, and blue subpixel elements are used to create the color image, the blue element contributes less than the red or green elements to spatial image quality. It would, therefore, be advantageous to decrease the relative display area allocated to the blue subpixels and correspondingly increase the relative areas of the red and green subpixels.
In addition, it would be advantageous to allocate disproportionate areas of certain color subpixels to compensate for color balance. It is often desirable, particularly in color displays with gray levels, to design the luminosity of each display subpixel so that when it is activated in conjunction with the other subpixels, a particular color is obtained.
Relative area is one of several factors which control the apparent luminosity of a given subpixel. By designing the display with different proportional areas allocated to each primary color, it is possible to achieve a particular desired mix of colors without necessarily changing the luminance or spectral characteristics of the individual subpixel substances themselves.